BILL payers have been warned they face one-off surcharges as well as annual hikes to their water rates in order to fund the super sewer.

Fresh from announcing bill rises of up to £100 per year between 2015-20, the company has now warned it is prepared to slap additional charges of £29 on rates from next year after the cost of the tunnel spiralled past the £4billion mark.

Company bosses said they need to rake in about £165million from homes and businesses served in London and the Thames Valley as land needed for the 15 mile-long tunnel, part of which is to be built from Carnwath Road in Fulham, is costing more than anticipated.

Hammersmith and Fulham Council leader Nick Botterill said: “Thames Water’s double-whammy of bill hikes at a time when household budgets are being squeezed like never before beggars belief.

“The financial and human cost of the super sewer is too much to bear and the Government and Ofwat must now block the scheme in the interests of 14million customers.”

The body that represents water customers in England and Wales also says the rise is not justified and would make things harder for people already struggling to pay their bills.

"The magnitude of the increase is not warranted in these circumstances," said Sir Tony Redmond, from the Consumer Council for Water. "It is the only water company, of which we're aware, which is actually planning to make this proposal to Ofwat. Some of the costs that may well have been unanticipated during 2009 could have been managed during the course of the whole period rather than facing them now."

The company says the rise is to cover the cost of preparing for the construction of the Thames Tideway Tunnel.